Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/ash.gyp

Index: ash/ash.gyp
diff --git a/ash/ash.gyp b/ash/ash.gyp
index a280c481140541fd8359b06c949e6c115b998831..43457bdda8828a4da88fbf38d15621cbd88ad6ce 100644
--- a/ash/ash.gyp
+++ b/ash/ash.gyp
@@ -108,6 +108,9 @@
       'common/shelf/overflow_button.h',
       'common/shelf/shelf_alignment_menu.cc',
       'common/shelf/shelf_alignment_menu.h',
+      'common/shelf/shelf_background_animator.cc',
+      'common/shelf/shelf_background_animator.h',
+      'common/shelf/shelf_background_animator_observer.h',
       'common/shelf/shelf_constants.cc',
       'common/shelf/shelf_constants.h',
       'common/shelf/shelf_delegate.h',
@@ -789,6 +792,8 @@
       'content/shell_content_state.h',
     ],
     'ash_test_support_sources': [
+      'common/test/material_design_controller_test_api.cc',
+      'common/test/material_design_controller_test_api.h',
       'desktop_background/desktop_background_controller_test_api.cc',
       'desktop_background/desktop_background_controller_test_api.h',
       'shell/toplevel_window.cc',
@@ -807,8 +812,6 @@
       'test/cursor_manager_test_api.h',
       'test/display_manager_test_api.cc',
       'test/display_manager_test_api.h',
-      'test/material_design_controller_test_api.cc',
-      'test/material_design_controller_test_api.h',
       'test/mirror_window_test_api.cc',
       'test/mirror_window_test_api.h',
       'test/overflow_bubble_view_test_api.cc',
@@ -914,6 +917,7 @@
       'common/display/display_info_unittest.cc',
       'common/material_design/material_design_controller_unittest.cc',
       'common/popup_message_unittest.cc',
+      'common/shelf/shelf_background_animator_unittest.cc',
       'common/shelf/shelf_locking_manager_unittest.cc',
       'common/shelf/shelf_model_unittest.cc',
       'common/shelf/shelf_navigator_unittest.cc',